The recommended technique to brush the outside surfaces of the teeth at the upper or the lower jaw is to place the toothbrush head horizontally between the lip and the dental arch with the brushing surface facing the dental arch, place the bristles above the gumline, apply gentle pressure against the gums with tiny horizontal movement to massage the gums and to dislodge the dental plaque and debris, sweep the bristles downwards along the length of the teeth towards biting ends.
The same technique is used for brushing the inside surfaces of the teeth at the upper and lower jaws. Due to the obstruction of the frontal teeth to the handle of the toothbrush, it is necessary to place the toothbrush and therefore its head inclining upwards for cleaning the inside surfaces of the molars and the premolars at the lower jaw and inclining downwards for cleaning the inside surfaces of the molars and premolars at the upper jaw. Also, it is necessary to use the toothbrush head vertically for cleaning the inside surfaces of the canines and incisors.
The conventional flat-trimmed toothbrush has a flat brushing surface but the human dental arches are of a general parabolic shape. When the conventional flat-trimmed toothbrush is used to brush the outside surfaces of the teeth, the contact area between the toothbrush and the dental arch is limited (FIG. 6). For the toothbrush, the contact area is mostly at the center line of the brushing surface. This often causes an unduly wearing of the bristles at that part (they bend out drastically and can not be easily straightened back). Bristles at other part of the head are less used and thus wasted. The limited contact area of the toothbrush on the dental arch makes brushing inefficient and thorough cleaning is not guaranteed even for people who do systematic and careful brushing. There could be areas on the teeth surfaces which would be left untouched by adjacent apparently overlapping brushing attempts traversing the dental arch. Because the gums also follow the parabolic shape, the limited contact of the flat-surfaced toothbrush with the gums means all the pressure applied to the gums by the toothbrush is concentrated at that small contact area. This causes excessive stress on the gums.
Generally, the tips of the bristles near the front end of a conventional flat-trimmed toothbrush have difficulty accessing the rear parts of the outside surfaces and gums of the second molars in adults and the outside surfaces and gums of the third molars are entirely unaccessible because of the obstruction to the toothbrush head caused by the frontal ridges of the rami of the lower jaw bone (41 in FIG. 6). The brushing surface of the conventional flat-trimmed toothbrush head is unable to reach the back surfaces of the last molars.
For brushing the inside surfaces and gums of the molars at the lower jaw, the flat-trimmed toothbrush is awkward to reach the area around the gumline. This is because the inside surfaces of the molars are inclined to the tongue. With the tongue in place, the toothbrush head has no room for further downward rotation to allow the brushing surface of the head to be in flat contact with the inside surfaces of the molars. When brushing the inside surfaces of the frontal teeth both at the upper and the lower jaw, with the toothbrush head placed vertically, the bristles scratch at the slanted parts of the inside surfaces of the teeth but may actually overpass the recessed areas around the gumlines. These are the shortcomings of the conventional flat-trimmed toothbrush.
Modifications to the shape of the brushing surface of the conventional flat-trimmed toothbrush to create a concave cylindrical contour to suit the dental arches are known in the prior art, for example, the Cheng toothbrush, U.S. Pat. No. 4,712,267, The Millar toothbrush, U.S. Pat. No. 5,315,731, the Humphries toothbrush, U.S. Pat. No. 5,465,450. All of these patents use the method of bending the back of a conventional flat-trimmed toothbrush head to create the designed concave (and convex in the patents of Cheng and Humphries toothbrushes but this will not be discussed here) cylindrical shape of the brushing surface.
A common problem for a toothbrush with a concave cylindrical brushing surface according to these designs is: due to the bending of the back of the toothbrush head, the bristles at the front end of the toothbrush (referred to herinbelow as the `front end bristles`) point backwards, so that the free ends of these bristles are at a greater distance to the foremost point of the toothbrush head (FIG. 7).
Therefore, the outside surfaces of the second molars now become even less accessible for brushing than in the case of brushing with the conventional flat-trimmed toothbrush of the same original shape due to this greater distance, the frontal ridges of the rami here being equally obstructive to the foremost point of the toothbrush head (FIG. 8). This is a serious drawback. This same drawback of the concave toothbrush of these designs makes the cleaning of the inside surfaces and gums of the back molars difficult. Besides, the user may find that a hump-backed toothbrush head of these designs appears too bulky when used in the buccal region.
A toothbrush head design of a different approach is needed to create a toothbrush which has a concave cylindrical brushing surface to suit the outer contours of the dental arches, and this novel toothbrush shall perform well in cleaning all aspects of the teeth as well as massaging and stimulating the gums, when used according to the recommended brushing technique, and it will not have the mentioned shortcomings of the toothbrushes of the bent-back designs. These are the features of the toothbrush head of the present invention.